1. Field of the Invention
The present invention relates to an organic luminescent display device, and more specifically, to a technology effective when applied to a top emission-type organic luminescent display device.
2. Description of the Related Art
Organic electroluminescence elements (hereinafter, referred to as “organic luminescent elements”) capable of spontaneously emitting light are expected to find applications in thin display devices and lighting devices for liquid crystal display devices.
An organic luminescent display device is formed of multiple organic luminescent elements forming pixels on a substrate, and a driver layer for driving the organic luminescent elements. The organic luminescent elements each have a structure in which multiple organic layers are sandwiched between a lower electrode and an upper electrode. The multiple organic layers are formed of at least a transporting layer for transporting a hole, a transporting layer for transporting an electron, and a luminescent layer in which the hole and the electron recombine. When a voltage is applied between both the electrodes, a hole and an electron injected from the electrodes recombine in the luminescent layer to emit light.
An improvement in efficiency of each of the organic luminescent elements is needed for reducing the power consumption of the organic luminescent display device. Light emitted from the luminescent layer of each organic luminescent element is exited toward an air layer. The refractive index of a general organic luminescent layer is around 1.8. Meanwhile, the refractive index of the air layer is 1. Accordingly, without exception, a total reflection interface exists, and light beams that propagate through the inside of each organic luminescent element exist. In the case of, for example, a top emission structure using an upper transparent electrode, total reflection light beams exist at an interface between the upper transparent electrode and the air layer, and about 80% of the light beams propagate through the inside of the organic luminescent element so as to be responsible for a reduction in efficiency of the element.
Japanese Patent Application Laid-open No. 2007-141728 discloses a structure in which a light-scattering layer is provided on an upper transparent electrode. Light beams to be totally reflected at an interface between the upper transparent electrode and the light-scattering layer are scattered so as to be taken in the air layer. By the method, however, even light beams that are not intrinsically scattered are scattered, and hence a light extraction effect may be at most about 1.5 times as high as that described above. That is, about 70% of the light beams propagate through the inside of the organic luminescent element.